This application claims priority of Japanese No. 2001-155214, filed May 24, 2001, the complete disclosure of which is hereby incorporated by reference.
a) Field of the Invention
The present invention relates to a thin outer rotor type brushless motor for use in a device to rotatably drive flexible discs, CD""s and the like and, more particularly, relates to a configuration of an armature core of the brushless motor.
b) Description of the Related Art
An outline of an armature core and a magnet portion of conventional motor 100 is shown in FIG. 6 with a cross section of one-half from the center.
In armature core 101, a plurality of pole teeth 102 are formed radially and a coil 103 is wound up in each of pole teeth 102.
Armature core 101 is mounted on the base 104 through a spacer 105 so as not to touch the base 104 directly.
A ring-shaped magnet 106 is concentric with the armature core 101 and is fixed on the outer circumference of disc 108 which can rotate with a rotating shaft 107 in the center which is supported on the base 104.
The clearance between an internal circumferential surface 106a and an outer circumferential surface 109a of salient poles 109 which are the tip of pole teeth 102 has a constant opening (air gap).
c) Problems to be Solved by the Invention
However, as miniaturization of a computer progresses, a small size of a disc drive device is expected and a motor for use in the above device is required to form a thin motor shape.
On the other hand, if the armature core 101 is made thin, magnetic flux H passing through the salient poles 109 of the armature core 101 decreases. Thus, the torque of a motor is reduced.
Additionally, if a wire size of coil 103 is made small in order to make the coil 103 thin, electric resistance increases so that current decreases and the torque of a motor is also reduced.
Furthermore, because a magnetic flux depends upon the number of turns of coil 103, a method for reducing the number of turns and the thickness also reduces the torque of the motor.
On the other hand, even if the magnetic force of the magnet is strengthened in order to reinforce the torque, the cross section of the armature core 101 is small so that magnetic flux passing therethrough causes saturation. Thus, enhancement of the magnetic force does not result.
Therefore, a primary object of the present invention is to offer a motor that has thinness and can provide a large torque.
In order to achieve the above object, a motor according to the present invention, fundamentally, a base to support rotatably with a rotor, a ring-shaped magnet having a magnetic pole segment which is S-pole shaped and a magnetic pole segment which is N-pole shaped are magnetized alternately in the circumferential direction, the ring-shaped magnet is fixed on the rotor, an armature core in which a plurality of pole teeth are formed radially and a coil is wound up in each of the pole teeth and the armature core which is mounted on the base to face an internal circumference of the ring-shaped magnet.
In the motor, first salient poles of the armature core, the tip of the first salient poles faces the ring-shaped magnet through an opening in the circumferential direction, second salient poles of the armature core, which extend in the circumferential direction from the tip of the second salient poles, which face the ring-shaped magnet through an opening in the axial direction.
In the ring-shaped magnet, the magnetic pole segment facing the first salient poles and the magnetic pole segment facing the second salient poles are magnetized by the same pole.
Furthermore, notching parts are formed on the base, into which notching parts of the armature core fits notching parts and the second salient poles of said armature core are fastened on the internal circumferential surface of the notching parts.
As described above, the motor according to the present invention can be thin and the area of the salient poles of the armature core facing the ring-shaped magnet can be made broadly so that the magnetic force of the ring-shaped magnet is stronger than that of the conventional motor.
Thus, the magnetic flux increases and can strengthen the motor torque.